NHC Wind Radii Forecast Considerations
The national hurricane center's forecast advisory details the current and forecast wind radii for the area of 34, 50 and 64 knot winds. Since many of the functions of the system utilize this data, there are several considerations the user need to be aware of.
1. Due to the squally structure of a tropical system, the winds vary greatly in each quadrant. While a portion of a quadrant may be experiencing sustained hurricane force winds other areas in that quadrant at the same radius may be sustaining a much lower wind speed.
2. The "observed" and forecast wind radii represent the largest radii of those winds in that quadrant. The reason for this is the same as indicated in #1.
3. The maximum winds and the radii winds being forecast represent sustained winds that are experienced from an open "ocean type" exposure. Due to the affects of friction, sustained surface winds over land are much less. Since the winds above the surface are not impacted as much by friction, land areas typically experience "forecasted" winds only during the passage of squalls... when these higher level winds are brought to the surface in the form of gusts.
4 .While 12 and 24 hour forecast are quite good, the NHC Average forecast error at 120 hours is over 250 nm. Care should be taken when utilizing forecast information past 24 hours.
5. The wind field within the eye wall is not uniform.. Many times one side of the eye wall is stronger than the other.